Rotary fluid equipment such as a centrifugal pump, usually includes a rotary operative member such as an impeller which is driven by a prime mover such as an electrical motor. A rotary shaft connects the prime mover to the operative member. Typically the operative member is contained within its own housing, having an inlet and an outlet for the fluid being moved, with the shaft passing through the back of the housing. The shaft may be supported by bearings and usually there will be seals engaging the shaft to prevent fluid which enters the housing from reaching the prime mover. The seals, shaft and seal housing define a seal cavity which opens towards the housing containing the operative member.
During operation, the fluid rotates within the seal housing, imparting a centrifugal force on any contaminant abrasives therein. The abrasives are thus thrown radially outwardly towards the wall of the cavity in the seal housing. Abrasive removal is normally accomplished by injecting a high flow of clean fluid into the cavity to force the abrasives away from the cavity wall and under the throat bushing for ejection. Normally, a dirty fluid cannot be used for fear of abrasives accumulating in the seal cavity. Typically, on a 2 inch shaft, about 4-6 gallons of clean fluid per minute is required to remove the abrasives, while only about 1/2 gallon per minute is needed to cool the mechanical seal faces. Using the current invention, the abrasives are presented at the best location for removal, allowing ejection by the low flow rate required for cooling. Considering the cost of sourcing clean fluid, the reduction of 1.5 to 2.5 million gallons per year per continuous running pump can result in appreciable savings. In addition, a dirty fluid can be used in high volumes, to achieve pressurization of the cavity to prevent seal damage due to flashing of high temperature fluids, without the risk of accumulation of abrasives in the seal cavity.
The current invention accomplishes this by providing a throat bushing or protector which has a face surface that slopes towards the throat from the area of the cavity wall to the area of the shaft. Preferably the sloping face will include at least one spiral groove into which contaminant material will be forced by the fluid flow in the seal cavity. Centrifugal force will hold the abrasive contaminant material in the groove, and the rotating fluid will drive it forward. As the abrasives are driven forward, the spiral winds inward, carrying them toward the shaft. At the shaft the abrasives will pass outwardly between the shaft and the bushing or protector of they can be guided into an optional groove on the inside axial surface of the throat bushing or protector which, with the help of a small fluid flow, guides the abrasives to the exterior of the seal cavity.
In seal cavities where the distance from the bore wall to the shaft is very small, the seal side of the throat bushing is sloped at a small angle to gently guide the abrasives radially inwardly. In seal cavities having larger cross sections, the gentle slope from the bore wall leads the abrasives to the spiral groove or grooves in the sloping wall of the throat bushing.